The Universal Serial Bus (USB) protocol has become a standard bus interface in computing devices that is used for many different applications. This interface is based on a broadcast mechanism wherein data is sent to all devices attached to a central host. The devices accept or reject the sent data based on the device address in the USB packet header. A significant drawback of this approach is that it leads to high Electro-Magnetic Interference (EMI) which necessitates the use of expensive shielding.
In accordance with another aspect of the USB 1.1 protocol, devices connect to the USB bus as either a Low Speed (LS) or a Full Speed (FS) Device. Due to the serial nature of the bus, the maximum bandwidth at LS is 1.5 Mbps. At LS, the protocol stipulates data payloads of 8 bytes, accompanied by 19 bytes of header information. This disadvantageously reduces the effective bandwidth.
Thus, there is a need for extension to the USB protocol that reduces the EMI problem and increases bandwidth at low speed while maintaining backward compatibility. The present invention provides such a solution.